1. Field of the Invention
The present invention relates to a wear-resistant material comprising carbon (C), nitrogen (N), oxygen (O), one or both of niobium and tantalum (Nb/Ta) as well as metallic elements and impurities as remainder. The material has a microstructure which comprises a metal matrix with hard phases embedded therein.
2. Discussion of Background Information
According to the technical approach, wear-resistant metallic materials comprise a tough or semi-rigid matrix and hard phases distributed therein, which phases are usually shaped as interstitial compounds.
A wear-reducing effect of hard phase inclusions is generally known, wherein a higher hard phase content in the matrix reduces an abrasive removal from the workpiece surface to the greatest extent possible when the support force for the hard material particles and the matrix hardness are high.
According to the prior art, wear-resistant iron-based materials, e.g. cold work steels, comprise a hard, preferably thermally hardened, metal matrix with carbides distributed therein that have been precipitated from the residual melt of the alloy during the hardening.
In a ledeburitic solidification of an alloyed melt in an ingot, a carbide formation may lead to coarse hard phases with inhomogeneous distribution in the material, due to a low rate of solidification in the center thereof and through segregation.
In order to attain a higher concentration of hard phases in the material, in particular with a uniform distribution in the material, it is known to use powder-metallurgical (PM) production methods. In this PM method essentially an alloyed liquid melt, after it has flowed out of a nozzle, is separated into small droplets by means of high-pressure gas jets, which droplets naturally cool at a fast rate and thereby precipitate fine hard phase particles during the hardening. Through a hot isostatic pressing (HIP) or by means of forming the powder in a container, a largely dense material with a high proportion of uniformly distributed hard phases with small grain size is produced.
However, increasing the wear resistance by raising the proportion by volume of hard phases in the matrix of a material and consequently raising the concentration of the elements forming the hard phases has limits in terms of process engineering and reaction-kinetics. During the course of atomization, primary precipitations in the liquid metal can lead to a reduction of their discharge from the nozzle or to a complete closing-off of the passage opening and thus have a disadvantageous effect on the producibility. A major alloy overheating in the supply vat of a metal powder production plant can also have metallurgical and/or reaction-kinetics disadvantages.
Due to the requirement for extremely wear-resistant materials that should optionally have a superior corrosion resistance, alloys have frequently been suggested that have a high content of carbide formers, in particular monocarbide formers, with a corresponding carbon content and a chromium concentration in the matrix of over 12.0% by weight.
For example, DE 42 02 339 B4, the entire disclosure whereof is incorporated by reference herein, proposes a corrosion-resistant, highly wear-resistant, hardenable steel with niobium contents of 5.0 to 8.0% Nb that can be produced without using a powder-metallurgical method.
In order to achieve a wear-resistant matrix with a hard, martensitic structure and a high carbide content even with slow cooling of a component, according to DE 10 2005 020 081 A1, the entire disclosure whereof is incorporated by reference herein, a high content of chromium, molybdenum, vanadium, and above all also nickel is provided, because these elements shift the pearlite nose to the right in the TTT diagram.
DE 42 31 695 A1, the entire disclosure whereof is incorporated by reference herein, discloses alloys in which no expensive chromium is to be lost through carbide formation and proposes to alloy a PM tool steel with 1 to 3.5% by weight of nitrogen.
Nitrogen for hard phase formation is proposed in WO 2007/024 192 A1, the entire disclosure whereof is incorporated by reference herein, as an advantageous measure for the production of wear-resistant materials.